Nonreciprocal quantum transport at junctions of structured leads

We propose and analyze a mechanism for rectification of spin transport through a small junction between two spin baths or leads. For interacting baths, we show that transport is conditioned on the spacial asymmetry of the quantum junction mediating the transport, and attribute this behavior to a gapped spectral structure of the lead-system-lead configuration. For noninteracting leads, a minimal quantum model that allows for spin rectification requires an interface of only two interacting two-level systems. In our paper, we have performed a thorough study of the current, including its time dependence and steady-state value. We obtain approximate results with a weak-coupling Born master equation in excellent agreement with matrix-product-state calculations that are extrapolated in time by mimicking absorbing boundary conditions. These results should be observable in controlled spin systems realized with cold atoms, trapped ions, or in electrons in quantum dot arrays.